In order to recover oils from certain geologic formations, injection of steam increases mobility of the oil within the formation via a process known as steam assisted gravity drainage (SAGD). The steam operates to heat the oil as the steam condenses at an interface with the oil that then drains to a producer well. Capital investments, operating costs and discounts on products recovered relative to West Texas Intermediate (WTI) limit payouts for applications based on the SAGD.
Steam generation costs represent a critical factor in these SAGD operations. A steam-to-oil ratio (SOR) provides a measure of steam requirements and is defined as amount of water needed to create the steam that is required to produce an equivalent volume of oil. Along with the steam generation costs, effectiveness of any recovery procedures determines economic feasibility.
One approach for producing the steam relies on conventional boilers or once through steam generators in which water being vaporized is isolated from burners. For greater efficiency, direct steam generation using oxy combustion quenched with water may also output the steam with carbon dioxide for injection into a reservoir. Based on reservoir simulations, accumulation of the carbon dioxide in the reservoir tends to lower the SOR but can decrease temperatures at the interface between the steam and the oil making production uneconomical.
Therefore, a need exists for improved methods and systems for recovery of oil from reservoirs.